Plant Virus Transmission by Insects

Abstract

Most plant viruses depend on vectors for their survival and spread. Most vectors are piercing‐sucking insects that transmit plant viruses in either the circulative virus (CV) or noncirculative virus (NCV). NCV are carried on the lining cuticle of vectors stylets. CVs cross the vectors’ gut, move internally to the salivary glands (SG), cross the SG membranes to be ejected upon feeding. Transmissibility of NCVs depends on motifs of coat protein and for Potyviruses and Caulimoviruses also on helper proteins (encoded by the virus). NCV proteins were found to associate with vectors’ cuticle proteins. Transmissibility of CVs depends on proteins comprising the virus capsid (the coat protein and the read‐through protein) and on symbionin (produced by vectors’ symbionts). Passage of CV through the gut has been also associated with vectors’ proteins. To suppress plant virus epidemics, several control measures that interfere with vector landing or feeding are proposed. Key concepts Plants are rooted; therefore, plant viruses depend for their spread on insect vectors Epidemics occur when a new virus or a new vector invade a new ecological niche. Specificity between viruses and vector species may reflect the preference of the vector to the plant species. Viruses that lost the ability to be transmitted by vectors serve to identify protein motifs that are associated with transmission. Noncirculative viruses are transmitted by aphids during intracellular stylet penetrations whereas circulative viruses are transmitted during committed phloem ingestion. Proteins encoded by the potyviruses and caulimoviruses are essential for assisting transmission by aphids. Heteroencapsidation is responsible for expanding the vector range of luteoviruses. Vector proteins were found to associate with viral proteins (for potyviruses, caulimoviruses and luteoviruses). Insecticide are inefficient in preventing noncirculative plant viruses spread by vectors (the time needed to kill the vector is longer than the time needed to inoculate the host). Control measures that affect vector landing or feeding are efficient in suppressing virus spread.

First outbreak of Pepper vein yellows virus infecting sweet pepper in Italy

“…Poleroviruses are transmitted by aphids in a persistent (circulative) and non-propagative manner (Raccah et al, 2009;Dombrovsky et al, 2010). To our knowledge, this is the first report of PeVYV in Italy.…”

Can Plant Viruses Cross the Kingdom Border and Be Pathogenic to Humans?

“…In contrast, animal viruses more evenly harbor RNA and DNA genomes, which are mainly monopartite, and a majority of virions have a spherical shape [ 11 ]. More practically, major differences exist between plant and animal viruses regarding the mechanisms they use to enter into cells and to then propagate from cell to cell [ 12 ]. Thus, specific interactions are implicated between animal viruses and cell receptors before viral entry into the cell by endocytosis or fusion, whereas viral egress from the cell occurs via cell lysis or through budding [ 13 , 14 ].…”

“…Notwithstanding these differences, breaking down the kingdom border is far from being unusual for some plant viruses. Indeed, ≈80% of known plant viruses depend on insect vectors for their transmission, although only a small proportion of insect-transmitted viruses are able to replicate in their insect vector [ 10 , 12 , 19 ]. The majority of these insect vectors are classified into the order Hemiptera , which notably encompasses aphids, whiteflies, thrips, leafhoppers and planthoppers [ 10 ].…”

“…For Potato yellow dwarf virus , the permissivity of insect cells depends on the presence of a glycosylated protein G [ 20 ], and for Rice dwarf virus a mutation of the P2 protein may abolish virus infectivity in the insect, and its transmission capacity [ 21 ]. There are two main modes of plant virus transmission by insects: non-circulative transmission, where the virus remains attached to the cuticle of the insect stylet or the anterior digestive tract of the insect vector but does not cross insect body barriers, and circulative transmission, where the virus crosses insect body barriers and enters its circulatory system and then accumulates in the salivary glands [ 12 , 22 ]. This specific viral adhesion to the cuticle can involve either capsid proteins that allow adhesion to insect receptors, as for Cucumber mosaic virus (CMV) [ 23 ], or through other viral proteins called helper components.…”

“…This specific viral adhesion to the cuticle can involve either capsid proteins that allow adhesion to insect receptors, as for Cucumber mosaic virus (CMV) [ 23 ], or through other viral proteins called helper components. In the case of potyviruses, one conserved domain (PTK) of the helper component protein (HC) has been shown to interact with a conserved capsid domain (DAG), and another conserved domain of HC is believed to interact with hypothetical receptors on the insect stylet [ 12 ]. In circulative transmission, infected saliva transmits the virus to healthy plants via insect feeding.…”